A wafer reader is a device used in the semiconductor manufacturing industry to read scribes from the surface of semiconductor wafers. A wafer scribe is an alpha-numeric code used to identify a wafer as it progresses through the manufacturing process. A scribe is marked onto the smooth surface of a wafer using a laser or diamond stylus. Typically the scribe is located on the surface of the wafer near a notch or flat edge on the perimeter of a wafer.
As they move from one manufacturing process to the next, wafers are commonly housed in a holding device called a cassette. One standard size cassette holds 25 wafers. A typical cassette has a series of shelves, equally spaced apart, such that each wafer rests on a shelf and is substantially parallel with the other wafers. The cassette is open on one side to expose a portion of the wafers and allow manufacturing equipment to access the wafers. Using the flat edge or notch on the wafer perimeter, a user or piece of equipment can align the wafers along the open side of the cassette.
Since cassettes are used extensively through the manufacturing process, the wafer reader should be able to read scribes from wafers located within the cassette. Some wafer readers available today can read scribes of wafers held in a cassette. One example of this type of wafer reader is described in U.S. Pat. Nos. 5,386,481 and 5,265,170 to Hine et. al. The wafer reader in these patents uses a wafer support that moves into position for each target wafer and displaces the adjacent wafers to expose the target wafer to read its scribe. While this type of wafer reader can read scribes from wafers in a cassette, it has a number of significant drawbacks.
One problem with the reader disclosed in the Hine patents is that it moves adjacent wafers apart to read scribes on the wafer surface. This particular aspect of the reader is disadvantageous because it tends to generate more particles, it is slow, and it requires relatively complex motion to read each wafer.
In the clean room environment of wafer processes, it is critical to avoid generating particles where possible. Readers that move one or more wafers to read a scribe generate particles by contacting adjacent wafers during the reading process.
An additional drawback of moving wafers during the reading process is that it takes more time for the reader to position itself to read each scribe. Since the wafer scribes may need to be read several times during manufacturing, a slower reading process will slow down the entire manufacturing process. In addition, a read operation that includes moving wafers requires more complex motion of the reader parts, making them more expensive and likely to fail.